It is well known to mount body/chassis accessories such as running boards, side bars or tube steps (referred to collectively herein as “step rails”) below the side doors of automotive vehicles such as pickup trucks and sport utility vehicles (SUVs) to provide a convenient step for use when entering/exiting the vehicle and for protection of the vehicle against side body damage. In addition, these step rails frequently serve as styling members intended to personalize or enhance the appearance of the vehicle. As such, both the mechanical strength properties and the external appearance properties of step rails are important. Further, since step rails are exposed to the rain, ice, mud, road chemicals (e.g., salt) and other harsh environmental materials, it is desirable that they be resistant to corrosion and/or surface finish degradation.
Conventional step rails are typically formed by bending tubular metal stock (e.g., where a tubular cross section is desired), by stamping flat metal blanks (e.g., where irregular, concave and/or convex surface features are desired), or by metal extrusion (e.g., where a constant cross section is desired). Commonly used materials for bending and stamping include steels, stainless steels and aluminum alloys, whereas extrusion in typically restricted to aluminum alloys. Ordinary steel step rails are typically painted, chrome plated, or powder coated to provide corrosion resistance and an attractive appearance. Stainless steel and aluminum alloy step rails may be left bare since those materials are inherently corrosion resistant, however, they are often polished to produce a reflective (i.e., “mirror”) finish or brushed to produce a matte (i.e., “brushed”) finish. Less frequently, they may also be painted or powder coated.
It will be appreciated that it is typically much easier (an hence, less expensive) to produce a high quality, uniform surface finish on basic metal stock (e.g., straight tubes, flat sheets, etc.) than it is on complex shapes such as a formed step rail. This is especially true in the case of bare metal finishes such as mirror and brushed finishes. Thus, it is desirable that the surface finish be applied to the basic metal stock before forming. However, the bending, stamping and extrusion processes conventionally used in forming step rails tend to mar, distort or otherwise damage the surface finish during forming. For low quality parts, such damage may be acceptable, given the savings in manufacturing costs. But for top-quality parts, even minor surface finish imperfections may cause the part to be rejected. Thus, the cost savings achieved by pre-finishing the stock may be lost due to a high defect rate in the finished product. A need therefore exists for a high quality formed step rail made from pre-finished stock using a process that will preserve the original high quality surface of the stock in the finished product.
It will also be appreciated that step rails must be strong enough to support the loads imposed upon them (e.g., the weight of passengers on the step) without failing, and be stiff enough to avoid undue deflection (“flexing”) and/or vibration during use. At the same time, it is desirable to minimize the overall weight and amount of material used in the step rail for performance and cost reasons. A need therefore exists for a formed step rail having a structural configuration that is relatively efficient, i.e., producing high strength and stiffness for the amount of material used.
After fabrication, the step rails must be mounted on the vehicle. This is typically accomplished through the use of bracket systems designed for the particular step rail/vehicle combination. However, ordinary variation in the location of the mounting holes provided on the vehicle by its manufacturer can sometimes make it difficult to install and adjust the step rails without requiring “field modification” of the bracket system and/or step rail itself. Such modifications are undesirable as they introduce additional complexity (and hence, additional cost) to the step rail mounting. Further, if done improperly, such modifications may also affect the structural integrity of the step rail. A need therefore exists for a bracket system which provides for uncomplicated installation and adjustment of the step rails even in the face of normal variation in vehicles.
While necessary for mounting the step rail to the vehicle, the bracket system is typically not considered a styling member. A need therefore exists for a step rail/bracket system combination which conceals as much of the bracket system as possible when viewed from normal viewing angles.